The internal combustion engine delivers power that is generally limited by the rate at which the fuel-air mixture can enter the combustion chamber and by the rate at which the exhaust products can be removed from the combustion chamber. Complicating this fairly simple equation is the fact that power demands, and thus intake and exhaust characteristics, differ between low speeds and high speeds.
Further complicating this equation is the fact that both good fuel economy and reduced emissions must be achieved. To this end designers and manufacturers of automotive vehicles have the common goal of developing and producing engine and combustion systems that improve fuel economy while also reducing undesirable system emissions. A variety of systems have been developed that achieve these ends to one extent or another. Such systems include modified combustion chamber configurations, finely-tuned amounts of fuel and air supplied to the combustion chamber, and intake and exhaust mechanisms that create desired tumble or swirl patters of the air-fuel mixture as it enters the combustion chamber.
With respect to demands for lower emissions and higher fuel economy on gasoline spark ignition engines, research has shown that accomplishing these goals often requires the use of active systems within the engine's air supply primary runners. These systems, which frequently include a rotatable valve located at a strategic point in the air intake duct, partially block the flow passage during light engine speeds and loads and open, eliminating the blockage as engine speed and load increase. The rotatable valve in such a design is thus located at a point where airflow is affected by low engine load and speed. By partially blocking the flow path air velocities and turbulence increase providing improved fuel and air mixing, combustion burn characteristics, and an overall improvement in fuel economy. An important factor in the generation of turbulence (and the consequent enhancement of burn rate in engines) is charge motion in the combustion chamber.
The size and shape of the flow blockage device is engine design dependent. It is ordinarily of a simple rectangular shape provided to block part of the flow pattern as it enters the cylinder. The intended result is to impart a swirling flow, a tumble flow, or a combination of these two flow patterns within the engine cylinder. However, these simple rectangular shapes are often incapable of delivering sufficient flow modification to provide the desired improvement in engine operation. The design is further complicated by the desire to be flow neutral when retracted at higher engine speeds and loads.
As in so many areas of vehicle technology there is always room for improvement related to optimizing the use of fuel in internal combustion engines.